The invention relates to an improved shim assembly for a disk brake which is incorporated into a disk brake used to brake a vehicle to reduce brake squeal produced by vibration of a pad in braking and to reduce uneven abrasion of a lining of the pad.
A disk brake used to brake a vehicle is structured such that a pair of pads are arranged across a rotor rotatable together with a wheel and, in braking, the pads are pressed against the two axial side surfaces of the rotor. The basic structure of such disk brake includes two types, that is, a floating type and an opposed piston type. In any structure, in braking, a rotor rotating together with the wheel is firmly pinched from the two axial sides thereof by a pair of pads. The two pads have their linings attached to the front surface of a pressure plate having sufficient rigidity. In braking, the pads press the back surface of the pressure plate to thereby cause the front surfaces of the linings and the two axial side surfaces of the rotor to rub each other.
Here, in the specification and claims of the invention, “an axial direction”, “peripheral direction” and “radial direction” mean, unless otherwise specified, the “axial direction”, “peripheral direction” and “radial direction” of a rotor when a shim assembly for disk brake is assembled to a disk brake. Also, “peripheral edge” means the “inner or outer peripheral edge” of the rotor in the radial direction.
In braking, a frictional force receiving portion, namely, a contact portion between the rotor two axial side surfaces and the front surfaces of the pad linings, and an anchor portion for supporting brake toque applied to the pads, namely, a contact portion between the pressure plate and a support or a caliper, deviate axially from each other at least by an amount equivalent to the thickness of the pad linings. And, according to the deviation amount equivalent to the thickness, the pads receive moment in a direction where the turn-in sides of the rotor approach each other (fall down on each other), whereby the attitudes of the pads are easy to be unstable. In braking, when the attitudes of the pads get unstable, the movements of the pads are hard to be smooth, thereby causing the pads to vibrate. Thus, noises called squeals can occur and the degree of uneven abrasion of the linings increases greatly.
To ease such squeals and uneven abrasion, conventionally, a shim plate is widely held between the back surface of a pressure plate constituting the pad and the tip end face of a piston or the inside surface of a caliper pawl part serving as a pressure surface for pressing such back surface. Such shim plate has a simple plate structure but, to enhance the squeal and uneven abrasion reduction effect, there is widely used a two-plate structure in which inside and outside shim plates are superimposed on top of each other. Also, there is conventionally known a structure in which the inside and outside shim plates are combined together such that, while being prevented against separation in the thickness direction, they can displace in the peripheral direction.
For example, the patent document 1 discloses a structure shown in FIGS. 9 to 12 as a two-plate structure shim assembly. In the illustrated example, a shim assembly 5 constituted of an inside shim plate 3 and an outside shim plate 4 is mounted on the back surface of a pressure plate 2 constituting a pad 1. The pad 1 is formed such that a lining 6 is attached and fixed to the front surface (which, when mounting the assembly to the disk brake, is opposed to the side surface of the rotor) of the pressure plate 2 with a large connecting force in a manner to be prevented against movement by brake torque applied in braking. The inside shim plate 3 is made of a metal plate and includes a flat plate-shaped inside shim main body 7 and three inside shim locking pieces 8a, 8b, 8c formed bent toward the pressure plate 2 in a total of three portions, namely, the peripheral-direction central portion of the outer peripheral edge and the peripheral-direction two near-to-end portions of the inner peripheral edge of the inside shim main body 7. The inside shim main body 7 has multiple opening-holes 9, 9 for holding grease. Also, the tip half portion of each of the inside shim locking pieces 8a, 8b, 8c is formed such that the axial-direction middle portion thereof is bent toward the peripheral edge of the pressure plate 2, thereby providing a substantially [doglegged] shape.
The pressure plate 2 includes, in the radial direction, an radially-outer-side locking recess 10 formed in the peripheral-direction central portion of the outer peripheral edge thereof, and a pair of steps 11, 11 formed in the peripheral-direction near-to-end two portions of the inner peripheral edge thereof. While the inside shim locking piece 8a on the radially-outer-side is engaged into the radially-outer-side locking recess 10 and the inside shim locking pieces 8b, 8c on the radially-inner-side are engaged into the steps 11, 11, the inside shim plate 3 holds the pressure plate 2 from both sides in the radial direction through the inside shim locking pieces 8a, 8b, 8c. In this state, the inside shim plate 3 is mounted on the back side of the pressure plate 2 while it is restricted (substantially prevented) against displacement in the peripheral and radial directions.
The outside shim plate 4 is made of a metal plate, and includes a flat plate-shaped outside shim main body part 12 and three outside shim locking pieces 13, 13b, and 13c. In the tip half portion of each of the outside shim locking pieces 13, 13b, and 13c as well, the axial-direction middle section thereof is bent toward the peripheral edge of the pressure plate 2, thereby providing a substantially [doglegged] shape. While the outside shim locking pieces 13, 13b, and 13c are overlapped with the inside shim locking pieces 8a, 8b and 8c respectively, the outside shim main body part 12 of the outside shim plate 4 are overlapped with the inside shim main body 7. In this case, the projecting portions of the tip half portion inner surfaces (surfaces opposed to the peripheral edge of the pressure plate 2) of the outside shim locking pieces 13, 13b, and 13c are elastically engaged into the recesses of the tip half section outer surface (surface opposite to the peripheral edge of the pressure plate 2). Thus, the outside shim plate 4 is mounted on the inside shim plate 3 in such a manner that it is prevented against separation in the axial direction (thickness direction) and can displace in the peripheral direction. For this purpose, the peripheral-direction width dimension of the outside shim locking piece 13a is set smaller than the peripheral-direction width dimension of the inside shim locking piece 8a, and the distance between the peripheral-direction outside edges (which are opposite to each other) of the two outside shim locking pieces 13b, 13c is set smaller than the distance between the two steps 11, 11.
In the above-structured first conventional structure, since the inside shim locking pieces 8a, 8b, 8c and the outside shim locking pieces 13, 13b, 13c are overlapped respectively, the amounts of projection of the outside shim locking pieces 13, 13b, and 13c from the peripheral edge of the pressure plate 2 are large. This requires consideration for interference with the other composing member of the disk brake, for example, a caliper. The restricted installation space of the disk brake requires large rigidity of the composing part such as the caliper. Thus, the need of consideration for interference prevention raises a disadvantage in securing the freedom of design of the disk brake.
In view of the above circumstances, for example, the patent document 2 discloses a shim assembly 5a shown in FIGS. 13 and 14 which can reduce the amount of projection from the peripheral edge of a pressure plate 2a. In the second conventional structure, of the two inner and outer peripheral edges of an inside shim main body part 7a constituting an inside shim plate 3a, in a total of three portions including the two peripheral-direction near-to-end portions of the outer peripheral edge and the peripheral-direction central portion of the inner periphery edge, there are formed inside shim locking pieces 8d, 8e and 8f respectively bent toward the pressure plate 2a. The front half portion inner surfaces of the inside shim locking pieces 8d, 8e formed on the radially-outer-side are respectively elastically contacted with the two locations of the two peripheral-direction near-to-end portion of the outer peripheral edge of the pressure plate 2a. Also, the front half portion inner surface of the inside shim locking pieces 8f formed on the radially-inner-side is engaged with an radially-inner-side locking recess 17 formed in the peripheral-direction central portion of the inner peripheral edge of the pressure plate 2a. 
On the two peripheral-direction ends of the inside shim main body part 7a, there are formed a pair of locking bent portions 14, 14 bent raised substantially at right angles toward the opposite side of the pressure plate 2a. In the width direction (radial direction) central portions of the base ends of the two locking bent portions 14, 14 to the middle locations, there are formed locking opening-holes 15, 15 respectively. In the near-to-tip ends of the two bent portions 14, 14, there are formed guide inclination portions 16, 16 respectively.
The outside shim plate 4a includes a flat plate-shaped outside shim main body 12a, three outside shim locking pieces 13d, 13e, 13f, and a pair of locking projection pieces 18, 18. The outside shim locking piece 13d formed in the peripheral-direction central portion of the outer peripheral edge of the outside shim main body 12a is engaged with an radially-outer-side locking recess 10a formed in the peripheral-direction central portion of the outer peripheral edge of the pressure plate 2a in such a manner that slight displacement in the peripheral direction is possible. The paired outside shim locking pieces 13e and 13f formed in the two peripheral-direction near-to-end portions of the outside shim main body 12a are respectively engaged with a pair of steps 11 formed in the two peripheral-direction near-to-end portions of the inner peripheral edge of the pressure plate 2a. The locking projection pieces 18, 18 formed projecting in the peripheral direction from the radial direction central portions of the two peripheral-direction end edges of the outside shim main body 12a are engaged with the two locking opening-holes 15, 15 of the inside shim plate 3a, thereby preventing the outside shim plate 4a against dropout.
In the second conventional example, with the above structure, the inside shim plate 3a is mounted on the back surface of the pressure plate 2a in such a manner that it is positioned in the diametric and peripheral directions; and, the outside shim plate 4a is mounted on the inside shim plate 3a in such a manner that it is positioned radially and can displace slightly in the peripheral direction. And, since the inside shim locking pieces 8d, 8e, 8f and outside shim locking pieces 13d, 13e, 13f are not overlapped radially, the amounts of projection of the outside shim locking pieces 13d, 13e, 13f from the peripheral edge of the pressure plate 2a can be reduced. Therefore, regardless of the structure of a disk brake, the shim assembly 5a and the other composing parts of the disk brake are made hard to interfere with each other, thereby enabling enhancement in the freedom of design of the disk brake.
However, in the above-mentioned second conventional structure, the bending direction of the two locking bent portions 14, 14 of the two peripheral-direction end portions of the inside shim plate 3a is opposite to that of the inside shim locking pieces 8d, 8e and 8f. This increases the number of working steps when the inside shim plate 3a is manufactured by press working, thereby increasing the working cost of the inside shim plate 3a. Also, the operation to engage the two locking projection pieces 18, 18 of the outside shim plate 4a with the locking opening-holes 15, 15 of the two locking bent portions 14, 14 is also troublesome, thereby raising a possibility of increasing the cost.
[Patent Document 1] JP 2006-200560 A
[Patent Document 2] JP 2013-061012 A